The primary causes of friction are surface roughness, the plowing effect and molecular adhesion. Surface roughness is when serious abrasion occurs due to the roughness of the materials in contact. The plowing effect involves deformations of the objects that cause resistance to movement when the materials are relatively soft.Continue Reading
Adhesion refers to the molecular force that results from two materials brought into close contact with one another. To slide objects against each other, it is essential to break the adhesive bonds between them. According to recent scientific studies, friction occurs because of adhesive forces between materials. Ultra-smooth and sticky materials fall under the molecular adhesion category.
There are varying degrees of surface roughness in solid materials. Even a smooth surface has small bumps that interfere with sliding motion. When the surfaces of two hard, solid materials are very rough, friction occurs due to the abrasion that happens when two objects slide against each other.
Deformations are another cause of friction. Deformations form when soft materials deform under pressure and lead to an increase in resistance to motion. For example, when a person stands on a rug, he sinks in slightly, causing resistance as he drags his feet along the rug’s surface. Resistive force is created, and friction occurs when the deformation becomes large.Learn more about Motion & Mechanics
When an object slides across the ground, it has much more surface area in direct contact with the ground, which means that the amount of friction is significantly higher. When an object rolls along the ground, only a minuscule point on the object contacts the ground at any point in time, making the stopping force much weaker.Full Answer >
The stopping, or braking, distance of a car is twice the original speed divided by the value of twice acceleration due to gravity, multiplied by the sum of the surface grade and the friction between the tires and the road. Braking distance is dependent upon speed and the roadway, so it varies in different situations.Full Answer >
Static friction is greater than kinetic friction because of irregularities between the static object and the surface upon which it rests. The irregularities mesh together making it more difficult to start movement than to keep the object in motion.Full Answer >
The coefficient of friction of rubber depends upon the surface in contact with the rubber. Rubber against rubber results in a static coefficient of friction of 1.15, whereas rubber against asphalt results in a static coefficient of friction of 0.9.Full Answer >